1. Field of the Invention
The present invention relates to a router supporting network mobility (NEMO) and a method for tunneling thereof. More particularly, the present invention relates to a router supporting network mobility over a nested mobile network and a method for tunneling thereof.
2. Description of Related Art
As the Internet is broadly and globally used in every field, the Internet access from mobile hosts or terminals in a mobile environment has become a necessity. Therefore, Internet Protocol (IP) mobility support for maintaining IP connectivity while a mobile terminal moves from site to site has attracted a lot of attention. In particular, IP mobility support for the mobile IP WG (Working Group) of IETE (Internet Engineering Task Force) has been actively discussed.
While the mobile IP WG has mainly focused on host mobility support, the NEMO WG in the IETF has been studied on the extension of existing mobile IP to support network mobility and considered a network, not a mobile host, as a mobile unit. For example, an NEMO protocol can be used in conjunction with any modes of transportation, such as automobiles, trains, planes, and ships, and mobile hosts in these means of transportation can be networked together.
In the case of NEMO protocol, a mobile router (MR), not a mobile host, becomes a mobile unit, and a mobile network that is formed around another MR can be a subnet to a higher level network. And, the subnet can have another subnet and/or mobile hosts. Here, when a mobile network has another subnet, it is said that the mobile network is nested. Depending on the situation, the networks can be more highly nested.
FIG. 1 illustrates the architecture of a nested mobile network over the Internet. According to the architecture shown in FIG. 1, there are four home agents HA_MR1-HA_MR4, four mobile routers MR1-MR4 included in the mobile network, mobile nodes MN, FN, and a correspondent node CN_FN2 on the Internet for conducting communication.
More specifically, the first mobile router MR1 includes the second and fourth mobile routers MR2, MR4 as its sub-nodes, and forms a mobile network Link1 together. In like manner, the second mobile router MR2 includes the second mobile host MN2 and the third mobile router MR3 as its sub-nodes, and forms a mobile network Link3 together. Likewise, the third and fourth mobile routers MR3, MR4, are linked to the mobile hosts MN3, FN2, MN1, and FN1, and form mobile networks Link4, Link2, respectively. That is, the network mobility enables a mobile network to have another mobile network therein.
The first to fourth home agents HA_MR1-HA_MR4 on the Internet are tunneled to the corresponding mobile routers MR1-MR4. Thus, through the tunnels, mobile network prefix information included in the mobile network are registered and forwarded for mutual packet exchange between the nodes existing in the mobile network and the correspondent node CN_FN2 on the Internet.
The first to fourth mobile routers MR1-MR4 forward a data packet transferred from the home agents HA_MR1-HA_MR4 to the mobile nodes within their own network, respectively, and transmit through the tunnel a data packet from the mobile nodes to the corresponding home agents HA_MR1-HA_MR4, respectively. When a mobile router becomes a lower level router of a certain mobile network, the lower level mobile router communicates with a higher level mobile router to receive a new address, and transfers the assigned address to its home agent.
Referring to the network architecture shown in FIG. 1, if the third mobile network Link4 formed around the third mobile router MR3 is newly transferred to the second mobile network Link3 formed around the second mobile router MR2, thereby forming a nested mobile network Link3, the third mobile router MR3 communicates with its higher level mobile router, the second mobile router MR2, to obtain an address, and sends a binding update message containing its address to the third home agent HA_MR3 within its home network. In this manner, the third mobile router MR3 is tunneled to the third home agent HA_MR3.
Here, the binding update message transmitted from the third mobile router MR3 is transferred over the Internet to the third home agent HA_MR3 via the second and first mobile routers MR2, MR1. Then, the second mobile router MR2 capsulates the transferred message, and transfers it to the first mobile router MR1. The first mobile router MR1 also capsulates the binding update message and transmits it to the Internet. At first, the binding update message on the Internet is transferred to the home agent HA_MR1, where the binding update message is decapsulated and is transferred to the second home agent HA-MR2. The second home agent HA_MR2 also decapsulates the received message and transfers it back to the first home agent HA_MR1.
On the nested mobile network, therefore, when a lower level mobile router sends address information to its home agent, the information or a data packet is repeatedly capsulated every time it passes through higher level mobile routers. Conversely, when a data packet is transferred from home agents of the higher level mobile routers to home agents of the lower level mobile routers, the data packet is decapsulated.
The same principle is applied to the packet transfer from a lower level node to a correspondent node on the Internet. In this way, the data packet from the home agent of a lower level node is finally transferred to a correspondent node which is the actual source of the data packet. The data packet transfer from the correspondent (i.e., corresponding) node to a final node of the lower level mobile network is exactly opposite to the above-described procedure. FIG. 2 diagrammatically illustrates a data packet transfer procedure from the correspondent node CN_FN2 on the Internet to the final node FN2 on the nested mobile network. Since the data packet transfer procedure from the correspondent node CN_FN2 to the final node FN2 of the lower level mobile network is opposite to the data packet transfer procedure described with reference to FIG. 1, a detailed explanation thereof is omitted.
FIG. 3 illustrates a header of the packet which is transferred from the correspondent node CN_FN2 to the final node FN2 of the mobile network as shown in FIG. 2. Originally in the packet header, the final node's address is entered as a destination address, and the correspondent node's address is entered as a source address, but later each home agent adds a corresponding mobile router's address to the destination address, and its own address to the source address, according to the sequence indicated by a digit number in FIG. 2.
However, a problem with the data packet transfer in the nested mobile network environment based on the related art NEMO protocol is that the data transfer takes more time than necessary due to the occurrence of repetitive capsulation and decapsulation. In addition, although the higher level mobile routers are not actually in charge of the transmission of a data packet from the lower level mobile router to its home agent, the home agents of the higher level mobile routers are respectively involved in the packet process. As a result, the transmission route is more complicated, and a so-called “pinball” routing problem occurs in the nested mobile network.
Moreover, even if a network is supposed to have an architecture for improving the network efficiency of the entire Internet as much as possible, the transmission route over the nested mobile network environment based on the related art NEMO protocol rather increases the traffic in the Internet and deteriorates the network efficiency of the entire Internet.